There is known a solid-state imaging device including a photoelectric conversion unit and a pixel circuit which are separately disposed on different substrates, and are electrically connected to each other via, for example, a microbump.
Japanese Patent Application Laid-Open No. 2009-170448 discusses a configuration in which an amplifying transistor and a selection transistor constituting a pixel circuit are disposed on a second semiconductor substrate, or only the selection transistor is disposed on the second semiconductor substrate.
In addition, Japanese Patent Application Laid-Open No. 2008-235478 discusses a solid-state imaging device including a first chip and a second chip. A plurality of light receiving pixels of the first chip is arranged on a light receiving surface, and generates electric signals according to incident light. Then, the electric signals of the light receiving pixels are transmitted to the back surface of the light receiving surface via through-wiring. A readout circuit is formed on the second chip. The readout circuit reads out the electric signals via the through-wiring, and outputs them as image signals. In this solid-state imaging device, the first chip and the second chip are disposed in such orientations that the back surface of the first chip and the readout circuit of the second chip face each other, and the terminals of the through-wiring and the readout circuit are electrically connected to each other. Japanese Patent Application Laid-Open No. 2008-235478 further discusses that a global electronic shutter is realized by providing, for example, a memory area for storing signal electric charges to each pixel, and a digital image signal is output by adding an analog/digital (AD) conversion circuit to each pixel.
However, the configuration discussed in Japanese Patent Application Laid-Open No. 2009-170448 is not sufficient to satisfy the functionality of solid-state imaging devices, which has been increasingly diversified in recent years. For example, a pixel additional circuit should be provided to, for example, expand the dynamic range, attain the electronic shutter function, and realize AD conversion at each pixel.
On the other hand, Japanese Patent Application Laid-Open No. 2008-235478 discusses that a pixel additional circuit such as a memory area and an AD conversion circuit is provided to each pixel. Further, Japanese Patent Application Laid-Open No. 2008-235478 discusses that the readout circuit disposed on the second chip is shielded from light.
However, Japanese Patent Application Laid-Open No. 2008-235478 fails to clearly describe the specific details of the light shielding structure. On the contrary, Japanese Patent Application Laid-Open No. 2008-235478 even discusses that it is possible to omit a light shielding layer or reduce the thickness of the light shielding layer since the upper portion of the readout circuit is covered with the first chip. However, the addition of the pixel additional circuit, which enables the expansion of the dynamic range, the attainment of the electronic shutter function, and the realization of AD conversion at each pixel, requires a more secure light shielding structure to be established.